1. Field of the Invention
The present invention relates to a method for producing a hologram of a light transparent type, and more particularly, to a method for producing a hologram capable of increasing a visible area during reproduction.
2. Description of Related Art
Known in the prior art is a hologram screen, where a light emitted from an indicator is irradiated onto a transparent screen on which a hologram is formed so that a recorded image is viewed on the screen. The transparency of the hologram allows the background to be viewed through the screen by the viewer. Thus, it is possible that this type of a hologram can be used at a customer counter of a bank or a hospital so that information about a customer or a patient is projected on the screen, while a receptionist sees the customer or the patient through the transparent screen.
Such an arrangement of the hologram may also be employed at an automobile retailer, where an advertising reproduction image is seen by a customer.
Furthermore, an application is also possible as a heads-up display for an automobile, which allows a driver to see a hologram image of various information such as vehicle speed in front of the windshield.
A light transparent type hologram screen is known, where a projector is arranged at a backside of a hologram screen so that a reference light is issued from the projector. A real image is created on the hologram screen, from which a diffraction light is diffracted, while the image is viewed by a viewer.
In order to produce such a hologram screen, a method is known where a light is passed through a light diffusing body such as a frosted glass plate to obtain diffuse light as an object light (signal wave), which works with non-diffuse light as a reference light (reference wave), so that an interference fringe is created on a photo-sensitive member.
It is, of course, desirable that the hologram screen has as wide a visible area as possible so that a viewer can view the hologram screen at various locations. In order to widen the visible area of the hologram screen, it is necessary to increase the expansion angle of the object light introduced into the photo-sensitive member by, for example, increasing the size of the light diffusion body or locating the light diffusion body adjacent to the photo-sensitive member.
However, production of a transparent type hologram screen of an increased visual range is difficult because the increased incident angle of the object light causes the reference light to be blocked by the light diffusing body, which prevents the photosensitive member from being illuminated by the reference light.